As a conventional example of the pipe joint, there are pipe joints which are shown in Patent Documents 1 and 2 listed below. The pipe joint of Patent Document 1 is structured such that a sleeve is pressed against an outer periphery of a pipe in a front side, and the pipe in the front side is connected to a pipe in a rear side by withholding it by a cover body which is screwed onto a main body (corresponding to a union nut). Further, loosening of the cover body is prevented by fixing the cover body to the main body by a connecting pin.
On the other hand, the pipe joint of Patent Document 2 is structured such that an adjusting joint is rotatably attached to an outer periphery of a leading end via a ball, and a nozzle tip is attached to a leading end of the adjusting joint by using a union nut (a cap nut). Because of such a structure, the union nut does not become loose even if the pipe joint and the adjusting joint are relatively rotated.
Further, a loosening preventing structure of a container plug which can be utilized as a countermeasure for loosening of the union nut is disclosed in Patent Document 3 listed below. In this structure, an outer periphery of a container neck and an inner periphery of a container cap are provided with ratchet gear teeth which mesh with each other, and when the cap is rotated in a closing direction, the gear teeth in the cap side moves on a leading surface of the gear teeth in the neck side so as to pass over the gear teeth in the neck side, whereas when the cap is rotated in a loosening direction, the gear teeth in the cap side moves on the trailing surface of the gear teeth in the neck side so as to pass over the gear teeth in the neck side.